1) Field of the Invention
The present invention relates to a particle-optical apparatus for manipulating a beam of charged particles, a method for operating such a particle-optical apparatus, a microscopy system and a lithography system.
2) Brief Description of Related Art
The particle-optical apparatus provides a magnetic field which the beam to be manipulated traverses. This manipulation may include a focusing, a deflection, a conversion of the beam or the like.
Magnetic field configurations are known from the prior art which have a focusing, deflecting or converting effect on a beam of charged particles.
For example, a beam deflector is known from U.S. Pat. No. 6,188,071 B1 for use in a lithography system. Here, a beam traversing the apparatus is an electron beam which is used as writing beam of the lithography system. A resolution of the lithography method performed therewith is thus determined also by the accuracy with which the deflection or/and focusing of the writing beam is performed in the apparatus. The apparatus comprises ferrite bodies for carrying the magnetic fields produced by current conductor windings. It is a property of ferrite materials that their magnetic permeability is temperature-dependent. Accordingly, if the temperature of the ferrite body changes, its magnetic property will also change and, correspondingly, the effects which the apparatus exerts on the writing beam traversing the same will change with temperature variations. According to U.S. Pat. No. 6,188,071 B1, a temperature control is provided to stabilize the temperature of the ferrite body in order to reduce influences of temperature on the quality of the lithographic process. It is also recognized in the document that the temperature regulation might, under certain circumstances, be too slow to sufficiently suppress temperature changes in the ferrite body. Therefore, the conventional apparatus comprises an additional correcting coil with low inductivity to actively compensate for the influences of the temperature dependence of the permeability of the ferrite material on the beam which are not completely suppressed by the temperature control.